The disclosure relates to roller levelers. It finds particular application in conjunction with roller levelers with independent work roll drive systems and various diameter eccentric work roll configurations, and will be described with particular reference thereto. However, it is to be appreciated that the present embodiment is also amenable to other like applications.
A roller leveler is used to achieve material flatness by precisely bending metal strip back and forth as it is passed through a series of offset work rolls to make the metal's surface flat, wave-free and to neutralize hidden internal stresses that cause twist and roll during secondary operations (e.g., stamping). The gap between the work rolls is set independently on a leveler's entry and exit. To begin leveling the metal, it is deeply “nested” upon entering the rolls—thereby forcing the material to plunge through extreme angles, removing strip memory caused by trapped internal stresses. Adjustable pressure points called flights under the rolls are used to raise and lower the rolls to a specific position—thus altering the material path length through the leveler and allowing the material to be stretched more because more work is being performed on it as it passes through the rolls.
A roller leveler typically includes multiple pairs of offset work rollers or rolls. Different size levelers can have different quantities of work rolls and back-up rolls. The upper rolls are typically offset one-half the distance between a pair of adjacent lower rolls. The metal strip passes between the upper and lower rolls. The number and spacing of the rolls depend on the thickness and strength of the metal strip. Typically, as the strip thickness decreases, the spacing of the rolls, as well as the roll diameter, decrease. As the strip passes between the rolls, it is bent up and down multiple times before it exits the leveler. The severity of the bend is greatest at the entry of the leveler and proportionately decreases towards the exit of the leveler. This reversed bending beyond the yield point of the material is the mechanism whereby the strip is flattened.
Metal is typically formed into strips by a process known as rolling, wherein the strip is passed between a pair of work rolls of a rolling mill to reduce its cross-sectional thickness. In the process, the strip is elongated and rolling continues until the strip is reduced to the cross-sectional thickness desired. This rolling process may start with heated billets or slabs of metal, wherein the metal is rolled at a very high temperature, or it may start with previously rolled strip wherein the strip is passed between work rolls in the cold state. In either event, when the strip exits from the mill, it may be convolutedly wrapped to form a coil. When the coil has been formed, curvature of the coil tends to stay with the strip when it is necessary to uncoil the strip for further processing. Thus, the primary problem with strip coming off of a coil is the curvature which remains with the strip and which varies throughout the entire length of the coil as a function of the radius of any particular portion of the strip while in the coil. Accordingly, the outer wrap of the coil will have less curvature than an inner wrap. To remove this variable curvature in the strip is one of the purposes of a roller leveler. It is necessary to remove this curvature so that the strip may be cut accurately and rendered suitable for other manufacturing operations, such as punching, drawing, forming and the like. It is well established that the flatter the strip is prior to a subsequent manufacturing operation, the more accurate and satisfactory will be the end product of that operation. Thus, even where portions of steel strip are deep drawn, they do not draw as satisfactorily if the strip initially is not substantially flat before the draw.
In addition to strip curvature, other unwanted properties are sometimes impressed upon the strip during hot and/or cold rolling which render the problem of flattening strip much more complex. In order to reduce cross-sectional thickness of the strip during rolling, it is necessary to force the strip between rolls under tremendous pressure whereby the strip essentially becomes a wedge which tends to separate the rolls. The force of roll separation is dependent upon the physical properties of the strip including width, thickness, hardness, temperature, yield strength, and amount of reduction being attempted during the pass of the strip between the rolls. If the work rolls are not sufficiently supported by back-up rolls, it is possible for the strip to actually cause the work rolls to bend at their centers, wherein the resultant strip cross-sectional shape is thicker in the middle than at the edges. Strip rolled with thicker center portions indicates that greater pressure has been applied to the edges of the strip than at the center, thereby causing the edges to elongate at a greater rate than the center of the strip. Because this excess metal on the edges must go somewhere, but is restrained by the center, the result usually is a product having what is referred to as edge waves. In other words, the center of the strip is relatively flat longitudinally, but the edges of the strip are sinusoidal.
A metal strip product is fed into a roller leveler, typically from a coil. Roller levelers use multiple work rolls of various diameters to flatten the strip as it passes through the leveler. The path of the strip passes between offset upper and lower work rolls, in effect reverse bending the strip multiple times before the strip exits the leveler.
A typical roller leveler is designed to process a range of strip thicknesses and strip yield strengths. As the strip passes between the work rolls, very high separating forces are generated against the work roll face, yet the work roll diameters are of necessity relatively small; this is to allow the work rolls to bend and to space them close enough to properly work the strip. The work rolls are supported by flights or groups of back-up rolls. The back-up rolls support the work rolls and prevent them from incurring excessive bending in reaction to the separating forces.
A problem with existing roller levelers is that a single drive system having a drive motor M and reducer R is used for multiple work rolls (see FIG. 1). Existing levelers L utilize distribution boxes D, which mechanically lock their work rolls together at the same fixed speed. However, in the leveler entry work rolls that are plunged deeper than the exit rolls must necessarily rotate at a different speed than the exit rolls. The speed difference of rolls accumulates into windup of the work roll spindles and increases the risk of roll-slippage/strip-marking and spindle or distribution box failure. Existing levelers install slip-clutches to limit windup, but they are expensive to calibrate and costly to stock for spares. If the drive train fails, then the entire leveler system capacity is reduced.
Existing roller levelers have a consistent geometry for the work rolls; meaning all of the work rolls are equally spaced and their outside diameter surfaces are coplanar or lie along the same plane. The aforementioned condition creates a uniform decrease in roll internmesh from the entry to the exit of the leveler. This, in turn, establishes the total horsepower required to do the leveling work. At the entry of the leveler, by altering the pitch between adjacent rolls or by altering the vertical height of adjacent upper rolls or adjacent lower rolls, horsepower requirements can be reduced substantially.
Another problem with existing roller levelers is that multiple diameter work rolls cannot be engaged at the same time. That is, only large work rolls or only small work rolls can engage the work piece but not at the same time. Thus, there is a need for a roller leveler system: i) which is comprised of independent work roll drive systems ii) which provides an eccentric roll configuration that varies the position of an entry roll (or rolls) in relation to the exit rolls which provides up to 20% more shape correction per horsepower, and iii) which provides a roll configuration that allows for large and small work rolls to both engage a work piece at the same time and extends the working gauge range of the leveler without having to change out roll cassettes or without requiring two separate levelers. The roller leveler system of the disclosure overcomes the above-mentioned deficiencies and others while providing better and more advantageous overall results.